144 ^ YEAR OF COST J RICAN NATURAL HISTORY 



hind edge, an outer, one-half to five-eighths inch long, an 

 inner one-eighth inch. I had often seen the species before 

 but it was not until I reached this laguna about noon that I 

 appreciated that numbers of this butterfly were traveling 

 all in the same direction. I was in a grassy lane about forty 

 feet wide, so I sat down to count the individuals which should 

 pass where I was, within this lane only, in a given time. 

 Between 12.07 and 12.12, I counted one hundred and forty- 

 four and I may easily have missed some. They came, not 

 continuously and at regular intervals but singly or in groups 

 of two, three, four, five, six, or almost any number up to 

 fifteen. They flew along at varying distances above the 

 ground, but all in the same direction — generally eastward — 

 and against the wind, which, when it blew a little stronger 

 now and then, gave them much trouble to beat against. 

 They did not stop to visit flowers or gather any other kind 

 of food but continued unceasingly their undulating flight 

 to the east. A few individuals of other species, as a bright 

 orange Callidryas or ally of Callidryas, seemed to accompany 

 the migrating species occasionally. To be able to identify 

 the species in the future, I caught three specimens, but the 

 first two had badly battered wings and I released them. 

 When set free they seemed disconcerted and started off 

 in new directions but within a minute or two changed their 

 flight to eastward. The condition of their wings implies 

 that the insects had not recently transformed from the 

 chrysalid state. As the butterflies flew toward me, when 

 I faced westward, it was impossible to foretell the exact 

 path which would be taken by any one individual, so great 

 was the lateral undulation in flight. 



When I left the spot where I had made the count, an hour 

 and a half later, there seemed to be no decrease in the num- 

 ber of the flying butterflies, so that 4320 of them must have 

 passed through that narrow lane while I was in its neighbor- 



